Method and apparatus for cutting a hole in the wall of a well



y 1967 J. H. MESSMER 3, 3,

METHOD AND APPARATUS FOR CUTTING A HOLE IN THE WALL OF A WELL Filed Dec. 28, 1964 United States Patent C METHOD AND APPARATUS FOR CUTTING A HOLE IN THE WALL OF A WELL Joseph H. Messmer, OHara Township, Allegheny County,

Pa., assignor to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Filed Dec. 28, 1964, Ser. No. 421,259

9 Claims. (Cl. 175-14) This invention relates to a method and apparatus for perforating, or cutting a notch in, a formation surrounding a Well, and more particularly relates to a technique utilizing wire line apparatus for cutting a hole of increased depth in a formation penetrated by a well.

It is the usual practice after drilling the borehole of a well to the desired de th to set casing in the well through the fluid-bearing formation from which production is to be obtained. The casing is cemented in place by displacing a slurry of a hydraulic cement, such as Portland cement, downwardly through the casing and upwardly into the annulus between the outer surface of the casing and the borehole Wall. The slurry of cement is held in the annulus until the cement sets.

After setting casing in a well, it is necessary to cut an opening through the casing and the surrounding sheath of cement to permit fluids to flow from the formation into the well. The openings may be perforations spaced from one another substantially throughout the interval of the fluid-bearing formation. Another method of providing the necessary flow channels into the casing is to cut a notch through the casing and cement and there-after pump a fracturing liquid down the well and through the notch under a pressure adaquate to rupture the formation rock and thereby create a fracture extending outwardly from the well into the surrounding formation.

Several methods are used to cut openings in casing to provide access between a well and the surrounding formation. One method of cutting the desired opening is to rotate or oscillate a mechanical cutting tool in the well to cut the desired opening by mechanical means. That method is slow and, because it usually requires a rotary rig at the wellhead, expensive. Another method of cutting openings in casing and in the surrounding formation is by bullets or shaped charges. The apparatus for cutting openings in casing by either of these means can be run into the well on a wire line; hence, the high cost incident to mechanical cutting is avoided. However, the penetration of the surrounding formation by bullets or shaped charges is generally limited.

Still another method for cutting openings in a formation surrounding a well is by discharging a slurry of abrasive particles in a liquid from a suitable nozzle suspended at the lower end of tubing run into the well from the wellhead. Cutting by means of a slurry of abrasive particles in a liquid incurs the expense of running tubing into the Well and of running and operating pumping equipment required for the high pressures needed to impart high velocities to the abrasive slurry. Moreover, the hydrostatic pressure exerted by liquid in the borehole of the well reduces the rate of cutting and the radial extent of the cut that can be made.

This invention resides in a method and apparatus for cutting an opening in a formation surrounding a well in which a capsule containing a solid rocket propellant fuel and having finely divided solid abrasive particles disseminated throughout the solid rocket fuel is run into a well on a wire line. The capsule is provided with a nozzle adapted to direct the products of combustion of the rocket fuel and the abrasive particles outwardly against the casing, if the well is cased, and the surrounding formation. The abrasive particles are graded through the fuel to change the abrasive discharged from the apparatus as burning of the solid rocket fuel continues to adapt the abrasive to the material being cut and thereby maintain a high cutting rate throughout the entire process. The rocket fuel is ignited to cut the desired opening in the wall of the well.

Referring to the drawings:

FIGURE 1 is a diagrammatic view, partially in vertical section, of a well having the capsule of rocket fuel in position to cut a notch in a surrounding fluid-bearing formation.

FIGURE 2 is a fragmentary vertical sectional view of the nozzle of the apparatus illustrated in FIGURE 1.

FIGURE 3 is a fragmentary vertical sectional view of an embodiment of this invention in which the combustion products and abrasive particles are discharged from the capsule through a rotating nozzle.

FIGURE 4 is a fragmentary vertical sectional view.

of apparatus for perforating casing in accordance with this invention.

Referring to FIGURE 1, a well indicated generally by reference numeral 10, is drilled through a fluid-bearing formation 12 into a base rock 14. Casing 16 is set in the borehole to total depth 18 and cemented in place 'by conventional cementing procedures to form a sheath 20 of cement surrounding the casing. The upper end of casing 16 is closed by suitable means illustrated by a cap 22 with a packing gland 24 extending upwardly therefrom. A capsule indicated generally by reference numeral 26 is run into the well to the desired depth on a wire line 28. Capsule 26 is provided at its upper end with a conventional wire line operated top hold-down anchor 30. In the preferred construction illustrated in FIGURE 1, capsule 26 has a series of sections 32a, 32b, 32c, and 32d below the holddown anchor. The sections 32a, 32b, 32c, and 32d are tubular members suitably threaded at each end for connection one to another and containing a mass 34 of a solid rocket fuel having particles of an abrasive material disseminated therethrough. A nozzle indicated generally by reference numeral 36 is connected to the lower end of section 320., as is best illustrated in FIGURE 2, and a plug 38 secured to the lower end of the nozzle provides a bottom closure for the capsule.

Nozzle 36 comprises an upper collar 38 and a lower collar 40 joined by spaced apart vertical webs 42. A nozzle insert 44 is secured to each segment of the upper surface of the lower collar 40 and the lower surface of the upper collar 38 between the webs to form a restricted opening which serves as the nozzle orifice 46. Because the stream of abrasive material discharged from the nozzle 36 flares outwardly in a divergent pattern, a circular notch the full 360 can be cut by means of nozzle 36. Nozzle inserts 44 are preferably made of a hard, heatand abrasion-resistant material such as tungsten carbide. In the apparatus illustrated in FIGURE 2, nozzle inserts 44 are shaped to form an outwardly flaring opening from the nozzle. With the outwardly flaring structure illustrated in FIGURE 2, erosion of the nozzle inserts results in gradual movement of the throat of the nozzle outwardly toward the casing.

In the apparatus illustrated in FIGURE 3, a nozzle indicated generally by reference numeral 4-8 is rotatably mounted in an upper bearing plate 50 secured to section 32d and a lower bearing plate 52 secured to plug 54. Nozzle 48 consists of a shaft 56 hollow at its upper end having a plurality of curved tubular nozzle arms 58 extending radially outward from the shaft 56. Openings extending laterally through the nozzle arms .58 com-municate 'with the central opening of the shaft 56. Shaft 56 is suspended by a lock nut '60 which rides on the upper surface of bearing 62 supported by the upper hearing plate 50. Leakage around the outer surface of shaft seminated' therein.

56 is prevented by a packing gland 64. The lower end of shaft 56 extends through lower bearing plate 52 which is supported on the shaft by a lock nut 66 and bearing 68. Pins 69 may extend from the outer surface of the bearing plate 52 to engage the casing 16 and thereby stabilize nozzle 48 as it rotates.

Rocket fuels suitable for use in this invention are composite rocket propellants composed of a mixture of an oxidizer and a reductant. Preferred reductants, which because of their plastic properties facilitate suspension of abrasive particles through them, are rubberlike combustible or plastic materials such as polysulfide synthetic rubbers, polyurethanes, polyvinyl chloride, polyethlene, polyester, and synthetic rubber. The reductants I are mixed with an oxidizing agent such as ammonium perchlorate or amomnium nitrate in proportions to provide suflicient oxygen for substantially complete combustion of the reductant. Double-base rocket propellants such as the plastic type propellants prepared from nitro cellulose and nitroglycerine are also suitable sources of fuel for use in this invention. Other rocket propellants suitable for. use in this invention are described in Rocket Propellant Handbookfby Kit and Evered, published by Macmillan Company, New York.

A slow 'burningrocket propellant is preferred as a fuelto avoid excessive buildup of pressure within the borehole. 'The burning, rate of the propellant can be controlled by any ofthe techniques conventionally used forcontrol of the burning rate of propellants for rockets. For example, the propellant can be in the form of grains which are coated with a slow burning material, generally referred to as an inhibitor. Propellants usuallyburn in a direction perpendicular to the, surface which permits the rated burning to be controlled by'reducing the surface. burning area of the propellant grains. A preferred arrangement for the propellant used in this invention is to castfthe propellant as a single block within each of the sections 32a, 32b, 32c, and 32dof capsule 26.

Because abrasive particles'difier widely in their ability to cut different solids, the abrasive'particles used in this invention are graded throughout the :mass of the solid rocket fuel to discharge fromthe nozzleabrasive particles best adapted to cutthe material to be cut by the abrasive at any particular stage of the cutting operation. For example, in the usual well completion in which casing is set through .the formation, the abrasive initially discharged @with the high velocity stream from the rocket fuel is an abrasive suitable for cutting steel casing. At a later stage of the cutting operation, the abrasive is one that is suitable for cutting the formation and the abrasive finally discharged from the nozzle is composed of rela- 1 Y tively large particles whichbecause of their large mass sections 32a, 32b, 32c, and 32d may contain a rocket fuel having a particular type and size of abrasive dis- The particular arrangement of the order of sectionscan then be selectedas required to prO- fvide most-efficient cutting of the materials that are to be penetrated.

The abrasive particles are disseminated throughout the solid'rocket fuel; in concentrations from about 2 up to 20- percent by 1Weight 0f the rocket fuel.

When the abrasive is a material of high density, such as steel pellets, the percentage by weight of abrasive is near the upper limi t of concentration. One advantage of disseminating the abrasive through the rocket fuel is that the abra-. sive acts as an inert mass which absorbs part of the heat particles, which have the advantage of low cost, are also effective abrasives for cutting such formations. The density of steel pellets makes them particularly effective in cutting the formation surrounding a well after the opening has been cut in the casing and especially advantageous during the latter stages of the cutting operation.

At the beginning of the. cutting operation, the material being cut'is close to the throat of the nozzle and the timefor solid particles to acquire a high velocity is limited. For this reason, it is desirable that the abrasive particles disseminated through the part of the rocket fuel burned during the early part of the cutting operation be small, for example, 40 to mesh in the US. Sieve Series or smaller. As the cutting proceeds and the surface struck by the abrasive particles is farther away from the throat of the nozzle, it is advantageous to use larger particles, for example, 20 to 30 mesh or 16 to 20 mesh, of abrasive.

In the apparatus illustrated in FIGURE 2 of the drawings in which the nozzle flares outwardly from the throat, the throat of the nozzle will move outwardly as the nozzle inserts 44 are eroded by the high velocity stream of combustion products and abrasive flowing through the nozzle. The arrangement has the effect of reducing the increase in stand-off of the nozzle from the surface being cut during the difficult period of cutting the casing. The gradual increase in the size of the nozzle orifice also allows larger particles of abrasive to be used in the latter portion of the cutting operation without danger of plugging the nozzle.

In the operation of the process of this invention, liquid is removed from the well by a suitable method such as swabbing. The wire line 28 is run through the cap 22 and connected tothe capsule 26 at the ground surface. The capsule 26 is lowered into the well, cap 22 is secured to the upper end of the casing, and the capsule lowered to the desired depth. If desired, the wellhead may be fitted with a lubricator of suitable size to allow the capsule to be lowered into the well with the cap in place on the .-upper end of the casing. The rocket fuel 34 is ignited by means of a conventional igniter connected to an electric lead 72., The rocket fuel 34 burns a combustible plate 74 at the lower end of section 32d and the products of combustion are discharged downwardly tothe throat 46 of the nozzle and radially outward therefrom against the casing. Burning of the rocket fuel proceeds upwardly successively through the sections 320, 32b, and 32a at a rate designed to impart a high velocity to the abrasive particles discharged through the throat 46' of the nozzle. The combustion gases are discharged from the casing through side outlet 25 at the upper end of the casing.

As the nozzle inserts wear down to the shape indicated by .the dotted line 76, the throat of the nozzle is enlarged and moved outwardly. The rocket fuel in the sections 32a and 32b can be a faster burning fuel to form combustion products at a rate compensating for the increase in the width of the nozzle orifice.

When this invention is used to cut a notch inthe formation to aid in fracturing the formation, the cutting of the notch is followed by filling the well with a liquid and withdrawing the capsule from the well. Suitable fittings are installed at the wellhead to permit pumping a fracturing liquid into the well and increasing the pressure on the liquid until the formation is ruptured. After a fracture has been initiated, a carrying liquid having a suitable propping agent suspended in it is pumped down the well and displaced outwardly from the well into the fracture.- The pressure in the well is then reduced and formation fluids that flow into the well are produced through the well.

In the apparatus illustrated in FIGURE 3, a high velocity stream of gaseous combustion products passes downwardly through shaft 56 into the arms 58 and is discharged against the casing and the surrounding formation. Arms 58 are curved to cause the nozzle 48 to rotate whereby interference of .the high velocity stream discharged from the nozzle with abrasive particles bouncing back from the surface to be cut is reduced.

In the apparatus illustrated in FIGURE 4 designed for creating a perforation in the casing, a simple nozzle insert 78 is secured .in the wall of the capsule below the lower end of the mass of rocket fuel. Upon ignition of the rocket fuel, a high velocity stream of combustion products and abrasive particles is discharged directly against the casing wall to cut a circular perforation in the casing.

This invention provides a method for rapidly cutting casing and a notch of substantial depth in the surrounding formation. The dissemination of abrasive particles throughout the rocket fuel results in a rate of cutting at least about five times the rate that can 'be obtained by a high velocity fluid stream without the abrasive particles. By increasing the size of the particles and their density toward the end of the cutting operation, the depth of cut that can be made in the formation is increased. The solid rocket propellant is advantageous in providing a definite combustible-oxidant composition that requires no elaborate equipment for controlling the burning rate in the borehole. Moreover, the solid propellant holds the abrasive particles in place until combustion occurs and thereby provides a simple and effective means of controlling the time at which abrasive particles of a particular type are discharged through the nozzle.

I claim:

1. A method of cutting an opening in the wall of a well comprising igniting a solid rocket propellant in a capsule supported in the well by a wire line, said solid rocket propellant having solid particles of an abrasive disseminated therethrough, burning the rocket propellant, and discharging the combustion products and entrained particles of abrasive outwardly at a high velocity across the wall of the well.

2. A method of cutting an opening in the wall of a well comprising igniting a solid rocket propellant in a capsule supported in the well by a wire line, said solid rocket propellant having solid particles of an abrasive disseminated therethrough, burning the rocket propellant, discharging the combustion products and entrained particles of abrasive outwardly at a high velocity across the wall of the well, and periodically changing the abrasive material entrained in the combustion products as required to maintain a high rate of cutting.

3. A method of cutting an opening in the wall of a well comprising burning successively a plurality of masses of solid rocket fuel in a capsule, said rocket fuel having abrasive particles disseminated therethrough, and discharging from the capsule through a nozzle the combustion products with said abrasive particles entrained therein outwardly against the wall of the well, at least some of said masses of solid rocket fuel having different abrasive particles disseminated therein than others whereby the abrasive particles discharged against the wall of the well are periodically changed to maintain a high rate of cutting.

4. A method of cutting an opening in the casing and surrounding formation of a well having casing set therein comprising running a capsule containing a solid rocket fuel into the well, said capsule having an outlet nozzle adapted to direct material passing therethrough outwardly against the casing, said rocket fuel having metal cutting abrasive particles selected from the group consisting of silicon carbide and aluminum oxide disseminated therethrough near the nozzle and abrasive particles of steel pellets disseminated therethrough more remote from the nozzle than the metal cutting abrasive particles, discharging combustion products having entrained therein said metal cutting abrasive particles to cut an opening in the casing, and thereafter discharging through said nozzle combustion products having said steel pellets entrained therein to cut an opening in the formation surrounding the casing.

5. Apparatus for running into a well on a wire line and cutting an opening in the wall of the well comprising a capsule suspended from the Wire line, an outwardly directed nozzle at the lower end of the capsule, a solid rocket propellant within the capsule, particles of an abrasive material disseminated throughout the solid rocket propellant, and igniting means adjacent the nozzle adapted to ignite the solid rocket propellant.

6. Apparatus as set forth in claim 5 in which the nozzle is rotatably mounted in the capsule and the nozzle has curved tubular arms extending outwardly adapted to rotate the nozzle as combustion products are discharged through the arms.

7. Apparatus for cutting an opening in the wall of a well comprising a capsule made up of a series of tubular sections connected one to another, each of said sections containing a solid rocket propellant having particles of an abrasive material disseminated therethrough, a nozzle opening from the capsule to direct combustion products outwardly against the wall of the well, and means for igniting the solid rocket propellant adjacent the nozzle, at least one of the sections forming the capsule having a different abrasive disseminated through the rocket propellant than the other sections whereby the abrasive material discharged through the nozzle changes during the cutting operation.

8. Apparatus for cutting an opening in the wall of a well comprising a tubular capsule adapted to be run into the well on a wire line, a solid rocket propellant in the capsule, a nozzle opening outwardly from the capsule toward the wall of the well, igniting means within the capsule adjacent the nozzle, and particles of abrasive disseminated throughout the rocket propellant, the particles of abrasive more remote from the nozzle being larger than the particles of abrasive closer to the nozzle whereby the size of particles of abrasive discharged through the nozzle increases as the cutting proceeds.

9. Apparatus for cutting an opening in the wall of a well comprising a tubular capsule adapted to be run into the well on a wire line, a nozzle opening outwardly from the capsule toward the wall of the well, a solid rocket propellant within the capsule, particles of a metal cutting abrasive selected from the group consisting of silicon carbide and aluminum oxide disseminated through the rocket propellant adjacent the nozzle and steel pellets disseminated through the solid rocket propellant more remote from the nozzle than the metal cutting abrasive whereby the metal cutting abrasive is discharged through the nozzle during the early part of the cutting operation and the steel pellets are discharged from the nozzle later in the cutting operation.

References Cited by the Examiner UNITED STATES PATENTS 2,265,982 12/1941 Bolton.

2,302,567 11/ 1942 ONeill 166-55 X 2,315,496 4/1943 Boynton 166-35 X 2,621,351. 12/1952 Piety 166-63 X 2,650,539 9/1953 Greene 166-63 X 2,680,487 6/ 1954 Carpenter 166-35 X 2,858,653 11/1958 Guptill 51-321 X 3,066,736 12/ 1962 Venghiattis 166-63 X CHARLES E. OCONNELL, Primary Examiner.

I. A. CALVERT, Assistant Examiner. 

1. A METHOD OF CUTTING AN OPENING IN THE WALL OF A WELL COMPRISING IGNITING A SOLID ROCKET PROPELLANT IN A CAPSULE SUPPORTED IN THE WELL BY A WIRE LINE, SAID SOLID ROCKET PROPELLANT HAVING SOLID PARTICLES OF AN ABRASIVE DISSEMINATED THERETHROUGH, BURNING THE ROCKET PROPELLANT, AND DISCHARGING THE COMBUSTION PRODUCTS AND ENTRAINED PARTICLES OF ABRASIVE OUTWARDLY AT A HIGH VELOCITY ACROSS THE WALL OF THE WELL.
 5. APPARATUS FOR RUNNING INTO A WELL ON A WIRE LINE AND CUTTING AN OPENING IN THE WALL OF THE WELL COMPRISING A CAPSULE SUSPENDED FROM THE WIRE LINE, AN OUTWARDLY DIRECTED NOZZLE AT THE LOWER END OF THE CAPSULE, A SOLID ROCKET PROPELLANT WITHIN THE CAPSULE, PARTICLES OF AN ABRASIVE MATERIAL DISSEMINATED THROUGHOUT THE SOLID ROCKET PROPELLANT, AND IGNITING MEANS ADJACENT THE NOZZLE ADAPTED TO IGNITE THE SOLID ROCKET PROPELLANT. 